Method for modifying plunge shaving cutters

ABSTRACT

A method for modifying plunge shaving cutters aims to modify a plunge shaving cutter through a grinding tool. The plunge shaving cutter has a plurality of helical teeth spaced from each other. The helical teeth have a machining-intended side. The method of modification includes the steps of: positioning the plunge shaving cutter on a gear forming grinder with the machining-intended side in contact with the grinding tool; moving the plunge shaving cutter according to a variable rotation amount and a first variable movement amount; moving the grinding tool according to a second variable movement amount to perform a helical movement against the plunge shaving cutter and a modification process on the machining-intended side. Thus the existing gear forming grinder can be applied to the plunge shaving cutter for machining to improve machining speed.

FIELD OF THE INVENTION

The present invention relates to a plunge shaving cutter andparticularly to a method for modifying plunge shaving cutters.

BACKGROUND OF THE INVENTION

Gears are fundamental elements for transmission of power and movement,and have the advantages of higher transmission efficiency, longerlifespan, safer, more reliable and the like, hence have becomeindispensable transmission elements in many machinery products.

Design and manufacture quality of the gears directly affect theperformance and quality of machineries. To meet higher qualityrequirement, the gear surface needs precise machining that mainly can beaccomplished by two types of methods, i.e. grinding and shaving. Thegrinding method can produce greater precision, but the grinding processis time-consuming and also generates a lot of oil smoke and grindingparticles, thus is less environmental-friendly and not economicjustified. Hence modifying the medium and high precision gears mostlyadopts the shaving technique. The shaving cutters can be repeatedlyused, and modifying the gear workpieces takes less time than thegrinding process, thus offers higher economic benefits.

U.S. Pat. No. 4,831,788 discloses a method and device for shaving toothflanks of shaving cutters. It adopts a rolling-generation method toshave the tooth flanks of the shaving cutters. But during the shavingprocess it requires additional steps of installing and disassembling theshaving cutters on the grinder. Japan publication No. JP2005-103749Aproposes another shaving method for shaving cutters. It provides arotary-gear-shaving-cutter grinder which comprises an upright machinepillar, a roller slide bracket movable linearly on the upright machinepillar, a spinning workpiece spindle located on the roller slidebracket, a transmission device to drive spinning of the workpiecespindle and linear movement of the roller slide bracket, a grindingwheel and an actuation device to drive the grinding wheel to rotate. Thegrinding wheel has a conical second work area to form a tangent contactwith the tooth addendum of the rotary gear shaving cutter for grindingin an undulant fashion to get a required crest circle diameter. Thus thecrest circle diameter of the rotary gear shaving cutter can be shrunk toa desired dimension.

However, after the shaving cutter has shaved the tooth surfaces of gearsfor a number of times, its cutting edge in contact with the toothsurfaces is gradually worn off that results in decrease of the toothprofile precision of the gears. Hence the shaving cutter has to bemodified. Moreover, the conventional five-axis shaving cutter grinder,such as the model Gleason-Hurth SRS 410 produced by U.S. Gleason Co.,adopts dry machining for modifying the shaving cutter. Its machiningspeed is slower, and the grinder has to be designed according to specialgrinding requirements of the shaving cutter, hence equipment cost ishigher. All these show that there are still rooms for improvement.

SUMMARY OF THE INVENTION

The primary object of the present invention is to solve the problems ofwearing off of the cutting edge of a shaving cutter after having shavedthe tooth surfaces of gears for a number of times that results indecrease of the tooth profile precision of the gears and dry machiningof the conventional five-axis shaving cutter grinder that results inslow machining speed and requiring a specially designed grinder forgrinding the shaving cutter to cause higher equipment cost for users.

To achieve the foregoing object, the present invention provides a methodfor modifying plunge shaving cutters implemented through a gear forminggrinder. The gear forming grinder includes a tool stand and a workpiecestand. The tool stand has a machining spindle to drive a grinding toolto spin. The workpiece stand is movable against the tool stand along afirst axis and has a workpiece spindle rotating about the first axis.The method comprises the steps as follows:

providing a plunge shaving cutter which includes a plurality of helicalteeth spaced from each other;

defining an machining-intended side on the helical teeth;

positioning the plunge shaving cutter on the workpiece spindle with themachining-intended side in contact with the grinding tool; and

spinning the grinding tool and rotating the plunge shaving cutter aboutthe first axis according to a variable rotation amount and moving theplunge shaving cutter along the first axis according to a first variablemovement amount at the same time, and moving the grinding tool along asecond axis perpendicular to the first axis and the machining spindleaccording to a second variable movement amount such that the grindingtool moves helically against the plunge shaving cutter to perform amodification process on the machining-intended side.

During the modification process, the ratio of the variable rotationamount and the first variable movement amount is a first variableobtained through calculation of a tooth profile parameter of the plungeshaving cutter, and the ratio of the second variable movement amount andthe first variable movement amount is a second variable obtained throughcalculation of the tooth profile parameter of the plunge shaving cutter.

Thus, the plunge shaving cutter of the invention can rotate about thefirst axis according to the variable rotation amount and move along thefirst axis according to the first variable movement amount, and thegrinding tool can also move along the second axis according to thesecond variable movement amount. Such a technique provides at least thefollowing advantages:

1. The grinding tool moves helically against the plunge shaving cutterto perform the modification process on the machining-intended side sothat the helical teeth whose tooth profiles have been modified can beused for shaving the teeth of the gears.

2. The variable rotation amount, first variable movement amount andsecond variable movement amount can be adjusted according to the toothprofile parameter of the plunge shaving cuter, hence the machiningamount of the grinding tool to the plunge shaving cutter can be evenlyadjusted according to the wearing condition of the plunge shavingcutter. The grinding tool uses wet grinding that can increase grindingspeed.

3. The invention uses the existing gear forming grinders, hence no extraequipment cost is required.

4. The invention not only can modify the conventional plunge shavingcutters, also can be used for grinding the new plunge shaving cutters.

The foregoing, as well as additional objects, features and advantages ofthe invention will be more readily apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the invention.

FIG. 2A is a schematic view showing the modification process accordingto an embodiment of the invention.

FIG. 2B is another schematic view showing the modification processaccording to an embodiment of the invention.

FIG. 3A is a schematic view showing a machining-intended side before themodification process according to an embodiment of the invention.

FIG. 3B is a schematic view showing a machining-intended side after themodification process according to an embodiment of the invention.

FIG. 4A is a chart showing a first variable according to an embodimentof the invention.

FIG. 4B is a chart showing a second variable according to an embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIG. 1 for an embodiment of the invention. It provides amethod for modifying plunge shaving cutters through a gear forminggrinder 1. The gear forming grinder 1 includes a workpiece stand 20 anda tool stand 10. The workpiece stand 20 is movable against the toolstand 10 along a first axis Z and has a workpiece spindle 21 rotatingabout the first axis Z. The tool stand 10 has a machining spindle 11, anupright movement portion 12, a swing portion 13 and a horizontalmovement portion 14. The machining spindle 11 spins about a third axis Xperpendicular to the first axis Z to drive a grinding tool 40 to spin.The grinding tool 40 is formed in a disk shape with an outer annularsurface 41 (referring to FIG. 2A) and a grinding edge 42 jutting andextending radially (also referring to FIG. 2A). The grinding edge 42 isconical and symmetrical on left and right. The grinding tool 40 can be,but not limit to, an emery wheel. The upright movement portion 12 iscoupled with the machining spindle 11 to allow the machining spindle 11to move along the third axis X. The swing portion 13 is coupled with theupright movement portion 12 to allow the upright movement portion 12 toswing about a second axis Y perpendicular to the first axis Z and thirdaxis X. The horizontal movement portion 14 is coupled with the swingportion 13 to allow the swing portion 13 to move along the second axisY.

Please refer to FIGS. 2A, 2B, 3A and 3B for an embodiment of theinvention in a modification process. The method of modificationaccording to the invention comprises the following steps:

Step 1: providing a plunge shaving cutter 30 which has a front endsurface 32, a rear end surface 33, a circumferential surface 34 and aplurality of helical teeth 31. The rear end surface 33 is remote fromthe front end surface 32. The circumferential surface 34 bridges thefront end surface 32 and rear end surface 33. Any two of the helicalteeth 31 are spaced by a backlash 35 and the helical teeth 31 arelocated on the circumferential surface 34. Each helical tooth 31 isextended from the rear end surface 33 to the front end surface 32 alongthe first axis Z in an oblique manner.

Step 2: defining a machining-intended side 311 and a cutting-intendedthickness 313 for the helical teeth 31. The machining-intended side 311includes a plurality of cutting blades 312 facing and protrusive towardsthe backlash 35. The cutting blades 312 are arranged along the firstaxis Z and spaced from each other, and have a greater thickness atpositions close to the front end surface 32 and rear end surface 33,thereby form an unmodified thickness 314 decreasing gradually inwardfrom the outer side. The cutting-intended thickness 313 is the thicknessto be modified from the unmodified thickness 314 of each cutting blade312 on the machining-intended side 311.

Step 3: positioning the plunge shaving cutter 30 on the workpiecespindle 21 so that it can be rotated about the first axis Z. Thegrinding tool 40 is moved via the horizontal movement portion 14, swingportion 13 and upright movement portion 12 to a contact-intendedposition. The plunge shaving cutter 30 is also moved from the workpiecestand 20 along the first axis Z to the contact-intended position. Thegrinding tool 40 is moved against the plunge shaving cutter 30 to letthe grinding edge 42 of the grinding tool 40 enter the backlash 35through the front end surface 32 of the plunge shaving cutter 30 tocontact with the machining-intended side 311.

Step 4: The workpiece spindle 21 controls the plunge shaving cutter 30to rotate about the first axis Z according to a variable rotationamount; meanwhile, the workpiece stand 20 moves the plunge shavingcutter 30 along the first axis Z according to a first variable movementamount, and the machining spindle 11 drives the grinding tool 40 tospin, and the horizontal movement portion 14 moves the grinding tool 40along the second axis Y according to a second variable movement amount,thereby the grinding tool 40 moves helically against the plunge shavingcutter 30 to perform a modification process on the machining-intendedside 311, and grinds the cutting blades 312 on the machining-intendedside 311. Thus a modified thickness 315 is formed by subtracting thecutting-intended thickness 313 from the unmodified thickness 314, andthe modified thickness 315 shrinks gradually inward from the outer side,and is smaller than the unmodified thickness 314.

Also referring to FIGS. 3A and 3B, it is to be noted that before themodification process the junctions of two flanks 316 and top edge 317 ofeach cutting blade 312 on the machining-intended side 311 have been wornto become a smooth curve after a long duration. In the event that aprecise tooth profile modification process is performed at this stage,the precision decreases to affect the quality and performance of thegear.

Hence, before the modification process, a tooth profile parameterrelated to the plunge shaving cutter 30 has to be set that can includebut not limit to the aforesaid cutting-intended thickness 313. Duringthe modification process, the variable rotation amount, first variablemovement amount and second variable movement amount are appropriatelyadjusted through the workpiece spindle 21, workpiece stand 20 andhorizontal movement portion 14 according to the set tooth profileparameter of the plunge shaving cutter 30 and grinding tool 40 so thatthe ratio of the variable rotation amount and first variable movementamount becomes a first variable a as shown in FIG. 4A, and the ratio ofthe second variable movement amount and the first variable movementamount becomes a second variable b as shown in FIG. 4B. The firstvariable a and second variable b form a nonlinear cubic curve as anexample, but this is not the limitation of the invention. Thus thecontact position between the plunge shaving cutter 30 and grinding tool40 can be adjusted, and the contact angle of the grinding tool 40against the plunge shaving cutter 30 also can be adjusted via the swingportion 13 to evenly modify the plunge shaving cutter 30 by subtractingthe cutting-intended thickness 313 of the cutting blade 312 to form themodified thickness 315 as shown in FIG. 3B. The junction of the top edge317 and flank 316 of the cutting blade 312 forms a cutting edge 318.

As a conclusion, the plunge shaving cutter of the invention can berotated about the first axis according to the variable rotation amountand also moved along the first axis according to the first variablemovement amount, and the grinding tool can be moved along the secondaxis according to the second variable movement amount to proceed ahelical movement against the plunge shaving cutter to perform themodification process on the machining-intended side, thereby the helicalteeth of the plunge shaving cutter can be modified further for a gearshaving operation. Moreover, the variable rotation amount, firstvariable movement amount and second variable movement amount can beadjusted according to the tooth profile parameter of the plunge shavingcutter to adjust each machining amount evenly of the grinding tool tothe plunge shaving cutter according to the wearing condition thereof toreduce error of the modified thickness. In addition, the grinding toolemploys wet grinding, hence grinding speed is faster. The invention canbe adaptable to the existing gear forming grinder without increasingextra equipment cost, hence it not only can be used for modifying theconventional plunge shaving cutter, also can be used for grinding thenew plunge shaving cutters. Thus the invention provides significantimprovements over the conventional techniques.

While the preferred embodiments of the invention have been set forth forthe purpose of disclosure, they are not the limitation of the invention,modifications of the disclosed embodiments of the invention as well asother embodiments thereof may occur to those skilled in the art.Accordingly, the appended claims are intended to cover all embodimentswhich do not depart from the spirit and scope of the invention.

What is claimed is:
 1. A method for modifying plunge shaving cuttersthrough a gear forming grinder which includes a tool stand and aworkpiece stand movable against the tool stand along a first axis, thetool stand including a machining spindle for driving a grinding tool tospin, the workpiece stand including a workpiece spindle rotating aboutthe first axis, the method comprising the steps of: providing a plungeshaving cutter which includes a plurality of helical teeth spaced fromeach other; defining a machining-intended side of the helical teeth;positioning the plunge shaving cutter on the workpiece spindle to makethe machining-intended side in contact with the grinding tool; andspinning the grinding tool and rotating the plunge shaving cutter aboutthe first axis according to a variable rotation amount and moving theplunge shaving cutter along the first axis according to a first variablemovement amount, and moving the grinding tool along a second axisperpendicular to the first axis and the machining spindle according to asecond variable movement amount such that the grinding tool moveshelically against the plunge shaving cutter to perform a modificationprocess on the machining-intended side; wherein during the modificationprocess a ratio of the variable rotation amount and the first variablemovement amount is a first variable obtained through calculation of atooth profile parameter of the plunge shaving cutter, and a ratio of thesecond variable movement amount and the first variable movement amountis a second variable obtained through calculation of the tooth profileparameter.
 2. The method of claim 1, wherein the tooth profile parameterincludes a cutting-intended thickness on the machining-intended side. 3.The method of claim 2, wherein the machining-intended side includes aplurality of cutting blades spaced from each other along the first axis,each of the plurality of cutting blades being formed at an unmodifiedthickness gradually decreasing inward from an outer side before themodification process is performed.
 4. The method of claim 3, wherein themachining-intended side includes a plurality of cutting blades spacedfrom each other along the first axis, each of the plurality of cuttingblades being formed at a modified thickness by subtracting thecutting-intended thickness from the unmodified thickness that graduallydecreases inward from the outer side after the modification process isfinished.
 5. The method of claim 1, wherein the machining spindle spinsabout a third axis perpendicular to the first axis, the tool standfurther including an upright movement portion coupled with the machiningspindle to move the machining spindle along the third axis.
 6. Themethod of claim 5, wherein the tool stand further includes a swingportion coupled with the upright movement portion to swing the uprightmovement portion about the second axis.
 7. The method of claim 6,wherein the tool stand further includes a horizontal movement portioncoupled with the swing portion to move the swing portion along thesecond axis.